The present invention relates to rare earth activated phosphors. Such phosphors are known to possess excellent light output and colour rendering properties and have been utilized successfully in many display technologies. One particularly successful material, europium activated yttrium oxide (Y2O3:Eu3+), has shown particular promise in the field of field emission display; yttrium oxide acts as a host for the Eu3+ or dopant ion.
The successful introduction of field emitting displays is dependent upon the availability of low voltage phosphors. As the phosphor exciting electrons have a comparatively low energy (less than 2 kV) as compared to conventional phosphors and one must avoid the use of sulphur to reduce contamination, new types of material have to be used. In particular, it is desirable to be able to make the phosphor particles without a surface dead layer which occurs when fine particles are prepared using a conventional grinding technique. This dead layer is an important source of non-radiative luminescence routes for low energy electrons.
According to the present invention there is provided a process for preparing phosphor particles of a host oxide doped with a rare earth or manganese without the need for a grinding technique which comprises:
preparing an aqueous solution of salts of the host ion and of the dopant ion and a water soluble compound which decomposes under the reaction conditions to convert said salts into hydroxycarbonate,
heating the solution so as to cause said compound to decompose,
recovering the resulting precipitate and
calcining it at a temperature of at least 500xc2x0 C.